SecureRandomSpi

This class defines the Service Provider Interface (SPI)
for the SecureRandom class.
All the abstract methods in this class must be implemented by each
service provider who wishes to supply the implementation
of a cryptographically strong pseudo-random number generator.

Causes the current thread to wait until another thread invokes the
notify() method or the
notifyAll() method for this object, or
some other thread interrupts the current thread, or a certain
amount of real time has elapsed.

engineNextBytes

If a call to engineSetSeed had not occurred previously,
the first call to this method forces this SecureRandom implementation
to seed itself. This self-seeding will not occur if
engineSetSeed was previously called.